Explosive cartridge



Aug. 21, 1951 R. w. LAWRENCE EXPLOSIVE CARTRIDGE Filed April 26, 1944 INVENTOR.

AT TORNEY FIG. 4

Pweea'r w LAWRENCE BY @wu- 2RM FIG.

FIGB

permissible tor coal mining.

cartridge to another'.

Patented Aug. 2l, 1951 UNITED STATES Parlato" oFF-lcs EXPLOSIVE CARTRIDGE Robert W. Lawrence, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation. ot Delaware Application AprilV 26, 1944, Serial No. 532,723

2 Claims. 1

This invention relates to a new and' improved explosive andY in particular to an ammonium nitrate explosive characterized by a low velocity of detonation.

In coal-mining operations permissible dynamites are widely used' because of their eiciency and relative safety. In most instances it is AdesiredV that coal be produced in lum-p form and notv excessivelyl shattered by the Iaction of the explosive. To accomplish this result, theforce of the explosion should be exeided more as a sustained heaving action rather than as a shattering effect. Such heaving action is Ycharacteristic of black powder explosives, which are. not classed as Two methods which have been employed to' achieve the desired type of. explosion from permissible dynamzitss are:

(l) use of an explosive with a lowV velocity of detonation, and (12) use of an explosive with a low density. Irr general, the velocity of detonation of the slow permissible dynamites: is of the order of 1.600 1:02300 m./sec. The densities vary from about 1 gram per cc., corresponding to 140 l 1px 8- inclr cartridges per'50.- pounds', tol about. 0.55 gram per cc., correspond-ing to a count oi 250 cartridges.

.Arttempts to.- reduce the. detonation velocity below about 11600 m./sec. by using very coarse irrgredients or by reducing the YpercentageA of nitroglycerin below 7 orv 8% are likely to result. in explosives which may fail to propagate from one For example. in explosives oi this type the sensitiveness is soflorw that the diameter or an explosive cartridge madef therefrom should not be; less than 11/2 inches in order tofinsure satisfactory propagation.

Decrease in density reduces the amount. of energy per unit volume of: explosive. Thus it frevcmently happens that after a moderate reduction inV density, there is insumcient explosive energy to do.` the required Work in 'a bore-hole of given size. inasmuch as reduction in. the density oi the explosive has only a limited application as a meansV of reducing shattering of coal, other methods of lowering the brisance have been sought; to accomplish this result.

In the past, explosive charges containing cylindrical or conical cavities in one. endv have been proposed to produce an intensified action ofthe explosive. This intensifiedaction.resultedy from a concentration or. the shock Wave and hot gases from the end of the explosive column on a very small area. Furthermore, these charges Were of dense highY explosive and: the intensified; action was limited toy a small area at the base off. the

charge. In a permissible dynamite, which is of relatively low density andI of low detonation velocity, such a cavity in the end of the cartridge would have only a small and very localized eiect.

Itis an'object-offthis invention 'to produce an explosiveof low' detonation velocity and decreased as a. special-aid in Vcoal-mining operations.. A further object is the production of a permissible dynamite which will haveV a decreased tendency to shatter coal. Still another object is the: production of an explosive which will' have a lovv` velocity of detonation and good propagation senstiveness'.

Generally described, this invention embodies cored cartridges of ammonia dynamite. These cartridges include an inert: core, formed by a tube or by va solid rod, and ammonia dynamite disposed about the core. The cartridges are then sealed in the conventional manner. The dynamite used in accordance with this invention is characterized by an inorganic nitrate composition of atleast In continuance oi this general discussionv of the nature and purpose of the invention, there follows` a more detailed description of preferred embodiments thereof with reference to the accompanying drawings;

Fig. l is a part-sectional, part-elevational View of a. conventional solid. cartridge of a permissible dynamite.

Fig. 2' is a part-sectional, part-elevational view of a hollow-cored cartridge of permissible dynamite, representing one form for the embodiment of the invention.

Fig. 3 is a part-sectional, partelevational view of" a solid-coredcartridige of permissible dynamite. representing anotherform for the embodiment of the invention.'

Fig. 4 is a part-sectional; part-elevational view of a filled-cored cartridge oi permissible dynamite, representing .still another form forthe embodiment of' this invention.

In Fig. l a conventional solid cartridge I of permissible dynamite. 2. contained. in the usual dynamite Wrapper 3. The explosive 2 is a permissible containing. at least 65% of inorganic nitrate.

In Fig. 2 a cartridge 4` has permissible dynamite 2 packed around la tube 5. The tube 5 may preferably be formed of: paper or a paper substitute, such as cellophane or ethyl cellulose. The cartridge is wrapped ina dynamite Wrapper 3.

,'In 3 a cartridge 6 comprises a permissible dynamite 2 packed. around a solid core 'lof Wood or plastic. 'I-he cartridge is Wrapped in a dynamite wrapper 3.

In Fig. 4 a cartridge 8 comprises a permissible dynamite 2 surrounding a tube 5, which is lled with a particulate inert or cooling material 9. Materials which may be used as fillers include sodium bicarbonate and gypsum.

As examples of ammonia dynamite compositions which may be used in carrying out this invention, the formulas in Table 1 are given.

To show the effect which application of the invention produces, detonation rates for permissible dynamites A, B, and C inv cartridges with and without the coaxial tubes, or hollowed cores, are compared in Table II. These compositions were packed into the space between an inner paper tube and the outer paper shell as shown in Fig. 2. After packing, the cartridge was crimped and used in the normal way.

TABLE II Eect of hollow coaxial tubes on the detonation rates of ammonia permissibles [8-inch cartridges] Outside Inside Average Ammonia Permissible Density Siggi g Dfga' eter eter Rates G./cc. Inches Inches M./scc. A 1. 1% l, 580 A 1.00 1% 54 1,410 B 0.85 1% 1, 590 B 0.85 1% 1,520 C. 0. 74 1% 1, 540 C, 0. 74 1% 3/4 1, 470 CV o. 74 1% 1, 370 C- 0. 74 1% }/2 1, 370 C 0. 54 1% 1, 510 C- 0. 54 1% l, 380 C 0.74 1% 1,730 C 0. 74 1% 1, 510 C 0. 74 2 l, 030 C 0. 74 2 l l, 395

Table III illustrates the effect of coaxial wooden dowels, as represented in Fig. 3, upon the detonation velocities of ammonia permissibles.

TABLE III Effect of a coaxial wooden dowl on the detonation rate of an ammonia permissible [Dynamite A, 8-inch cartridge] Wooden Cartridge Detona- Diameter Djigr tion Rate Inches Inches M ./scc. 1% None l, 635 1% M 1, 430

4 TABLE IV Effect of a coaxial tube filled with NaHCOs on the detonation rate of an ammonia permissible [Dynamite A, 10inch cartridge] Weight Outside Inside of Density Detona- Density Tube Tube NaHCOa of x tion Dia. Dia. in NaHCOs logive Rate Tube p G./cc. Inches Inches G. G./cc. G. M ./sec. l. 00 1% None None None 198 1, 640 1. 00 1% 87 l. 23 212 l, 470

It will be noted from Table IV that for an approximately equal charge weight of explosive a substantial lowering of the detonation velocity was effected by using a cored cartridge containing a cooling material, such as sodium bicarbonate, in the coaxial tube.

In Tables II, III, and IV a substantial lowering of the velocity of detonation is shown for the cartridges containing hollowed cores, sodium bicarbonate-lled cores, or wooden dowels. This lowering of the velocity of detonation varies with the relationship between the diameter of the core area and the diameter of the cartridge. A cartridge of any of the types illustrated in Figs. 2, 3, and 4 should have a minimum core diameter of about 1/4 inch to produce a lowering of the detonation velocity. A wall thickness of inch as a minimum is essential for the explosive column. As a preferred maximum outside diameter, 2 inches is given, although use of a larger diameter with corresponding adjustment of the thickness of the explosive column would not be outside the scope of this invention.

It is understood that the invention may take any of the forms illustrated in Figs. 2, 3, and 4. That is, the cored area may be (1) hollow, (2) filled with an inert or cooling material, or (3) filled with a solid core. The hollow core may be formed, as shown in Fig. 2, by a paper tube or a tube of any similar material, such as cellophane or ethyl cellulose. The embodiment shown in Fig. 3 contains a solid core of an inert material, such as wood or plastic. For cartridges of the type of Fig. 4 inert or cooling materials may be used to ll the cored space. Examples of such materials, inert with respect to the propagation of the detonation wave, are sodium bicarbonate, fine ammonium nitrate, ground gypsum, borax, plaster of Paris, calcium fluoride, and a mixture of ammonium chloride and sodium nitrite in equal molecular proportions. These materials may be used in particulate form or may be molded into a solid core. It will be understood that the use of such materials may aiect the oxygen balance of 'the explosive. However, an adjustment of the explosive composition is Well Within the province of a person skilled in the art.

This invention is applicable to ammonia dynamites having approximately the following composition ranges: nitroglycerin, 6-20%; inorganic nitrates (including ammonium and sodium nitrates), 65-85%; carbonaceous material., 4-l2%; chalk, 0.5%. Densities will vary between 0.55 and 1.40 g./cc. The detonation velocities of such explosive compositions in solid cartridges of the type shown in Fig. 1 are in the range of from 1500 to 3500 m./sec.

The preferred compositions for embodying this invention are, however, of the permissible dynamites class and contain the following proportions of ingredients: nitroglycerin, 7-14% ammonium nitrate, 60-80%; sodium nitrate, 5-15%; carbonaceous ingredients, 8-12%; chalk, 0.5%. For the ammonium nitrate, a particle size such that substantially all the particles are held on a 60-mesh screen is preferred. However, finer ammonium nitrate may be used if desired. The densities of these explosive compositions are in the approximate range of from 0.55 to 1.10 g./cc. The detonation velocities are usually between 1500 and 2500 m./sec.

The reduction of detonation Velocity as effected by the inert core running the length of the permissible cartridge appears to depend upon a reduction in the effective diameter of the cartridge. Thus, in explosives of this type, the detonation velocity is a function of the cartridge diameter. For example, in cartridges of 11/4 inch diameter and with explosive compositions similar to A in Table 1, the detonation velocity is about 1600 m./sec., whereas in those of 78 inch diameter it is about 1250 m./sec., and in those of inch diameter, about 1000 m./sec.

A particular advantage of the inert core is that it reduces the velocity of detonation without greatly decreasing the total quantity of explosive. For example, 11A, inch-diameter cartridge with a 1,41 inch-diameter core has only about 5% less explosive than a solid column of the same outside diameter. Thus, the effect of the inert core is to produce a cored explosive column whose thickness controls the velocity of detonation. When the thickness of the explosive column is too small, however, failure to propagate may occur.

As a further advantage, by causing a reduction of the detonation velocity of a permissible dynamite, this invention brings about a reduction in the shattering action of such a dynamite when it is used in coal mining. Another advantage in cartridges of the air-core type resides in the corespace, which may be advantageously utilized for positioning of a blasting cap. In view of these advantages, the invention herein described will be found particularly useful in coal-mining operations, where it is desired to produce lump coal. An explosive with substantially a heaving action also finds application in some quarrying and similar dynamiting operations in which a shattering effect is to be avoided.

Where, in the specification and claims, the term inert core is used, it is meant to include a hollow core or a solid or lled core in which the core materials utilized are inert with respect to the propagation of the detonation wave.

What I claim and desire to protect by Letters Patent is:

1. A permissible dynamite cartridge of decreased detonation velocity and decreased brisance having in combination a cylindrical wrapper, a cylindrical charge of permissible dynamite completely enclosed within the wrapper, saidV charge having a hollow coaxial core at least 1A; inch in diameter and a wall thickness of at least inch, said charge comprising between about 6 and about 20% nitroglycerin and between about and about 85 inorganic nitrate.

2. A cartridge according to claim 1 in which the hollow coaxial core is formed by a tube extending throughout the cylindrical charge.

ROBERT W. LAWRENCE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 58,656 Lucas Oct. 9, 1866 905,336 Lheure Dec. 1, 1908 1,502,646 Hedin July 22, 1924 2,463,709 McFarland Mar. 8, 1949 FOREIGN PATENTS Number Country Date 356,864 France Oct. 20, 1905 106,311 Great Britain May 15, 1917 440,273 Germany Jan. 29, 192'7 OTHER REFERENCES Marshall, Explosives, volume 2, pages 483, 486 and 487, 2nd edition, 1917. 

